The main sources of stress to corn from the time it is planted until the seedling emerges are:
- soil temperatures (usually cold)
- soil moisture (excess or lacking)
- inadequate soil aeration (ex. compaction, saturation)
- or a combination of all these factors above
Typically we would like to plant corn when air temperatures are 50 degrees F., with soil temperatures around 50 to 55 degrees F. at planting depth. Seed germination occurs when air or soil temperatures reach 68 to 77 degrees F. With the cooler temperatures in the weather forecast, we continue to see that many (especially those to the North) are concerned about cold injury at corn germination or cold imbibitional chilling damage.
When a corn seed first germinates, the seed absorbs 30 percent of its weight in water and thus, the radical or (first root) emerges. Some sources say at this stage of the germination game, soil temperature swings have no effect on growth and emerged seedlings are relatively resistant to cold.
There are many theories as to what causes cold imbibitional chilling damage, but one of the main theories is that injury occurs to the corn seedling when there are soil temperatures swings (some sources say less than 50 degrees and others say at least 41 degrees or below) after germination (24 to 36 hours after the seed has (imbibed) absorbed water). Soil temperatures for Illinois and Missouri can be easily found at www.burrusseed.com. If the cells of the corn kernel are too cold, they can rupture, thus the kernel can become swollen and any growth of the kernel can cease. Cold imbibitional symptoms may be delayed emergence, failure of emergence, leafing out underground, or stunted growth and distorted leaves of the newly emerged seedling (picture below).